Cambridge Secondary (7-9). Stage 8. Science. Learner's Book - Unit 2: Properties of materials

With a partner: explain the differences between an element, a compound and a mixture; share your answers with the class.

With a partner: draw a diagram of the way particles are arranged in a liquid; share your answers with the class.

Think like a scientist: Dissolving and mass
You will need: top pan balance; filter paper; salt; stirring rod; beaker of water.
Method
1 Place the filter paper on the top pan balance. Measure and record its mass.
2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt.
3 Remove the paper and salt from the balance.
4 Place a beaker containing at least 100 cm³ of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution.

Think like a scientist: Dissolving and mass
You will need: top pan balance; filter paper; salt; stirring rod; beaker of water.
Method
1 Place the filter paper on the top pan balance. Measure and record its mass.
2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt.
3 Remove the paper and salt from the balance.
4 Place a beaker containing at least 100 cm³ of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution.

What was the mass of salt used?

Think like a scientist: Dissolving and mass
You will need: top pan balance; filter paper; salt; stirring rod; beaker of water.
Method
1 Place the filter paper on the top pan balance. Measure and record its mass.
2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt.
3 Remove the paper and salt from the balance.
4 Place a beaker containing at least 100 cm³ of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution.

What was the mass of the water and the beaker?

Think like a scientist: Dissolving and mass
You will need: top pan balance; filter paper; salt; stirring rod; beaker of water.
Method
1 Place the filter paper on the top pan balance. Measure and record its mass.
2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt.
3 Remove the paper and salt from the balance.
4 Place a beaker containing at least 100 cm³ of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution.

What was the mass of the solution and the beaker?

Think like a scientist: Dissolving and mass
You will need: top pan balance; filter paper; salt; stirring rod; beaker of water.
Method
1 Place the filter paper on the top pan balance. Measure and record its mass.
2 Add about 20–25 g of salt. This is the solute. Measure and record the mass of the salt.
3 Remove the paper and salt from the balance.
4 Place a beaker containing at least 100 cm³ of water on the top pan balance. Measure and record the mass of the water and the beaker together. The water is the solvent.
5 Add the salt to the water. Stir until all the salt has dissolved. Measure the mass of the beaker and salt solution.

What does this tell you about the salt solution?

In a solution of sugar and water, which is the solvent and which is the solute?

What is the difference between dissolving and melting?

What mass of salt solution is made when 9 g of salt is dissolved in 50 g of water? Explain how you worked out your answer.

A green powder was placed into a beaker of water. After it was stirred, the water looked cloudy and lumps of powder could still be seen. Has a solution been formed? Explain your answer.

When measuring the volume of a liquid, what should you do in order to make your measurement as accurate as possible?

You have one minute to think about the meanings of the words solvent, solute and solution. You have one minute to discuss them with a partner. Now write your meanings on different pieces of paper. Share them with the class.

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

What do you notice about the solutions?

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

How can you tell which is the least concentrated?

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

If you repeated this task using a salt or sugar solution, would you be able to identify the most and least concentrated solutions? Explain your answer.

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

Why is it important to measure the food dye solution and the water accurately?

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

If you only had a measuring cylinder that measured up to 100 cm³, would using these same volumes of copper sulfate and water be accurate?

Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.

Compare the number of particles of food dye in the most concentrated solution of food dye and the most dilute solution.